1. Field of the Invention
The present invention relates to a device for detecting a puncture in an automobile tire. More particularly, the invention relates to a puncture detecting device in which a spring plate member is disposed in a pressure chamber defined by a flexible diaphragm, and is held in communication with the interior of a tire. A magnet is carried on a front face of the spring plate member. The spring plate member is normally maintained in a retracted position against resiliency, by the air pressure in the pressure chamber, to thereby hold the magnet away from an alarm circuit switch adapted to be actuated by magnetic force. The spring plate member is buckled so as to rapidly project forwardly under the resiliency when the air pressure in the pressure chamber decreases below a predetermined amount due to puncturing of the tire, whereby the magnet is moved closer to the switch to energize the same.
2. Description of the Art
A variety of puncture detecting devices have been known and proposed in which a magnet is resiliently supported and normally retracted by air pressure from the interior of a pneumatic tire, the magnet being forwardly movable closer to a switch of an alarm circuit in response to a reduction in the air pressure in the tire, whereupon the alarm circuit is actuated.
Such puncture detecting devices are generally built in a rim having a relatively large width. It has been difficult to mount the devices on a relatively narrow rim. Such known puncture detecting devices are affected by speed, and thus become too sensitive due to centrifugal forces when the rim revolves at high speeds. Furthermore, because the devices are mounted in a space in the rim, they are subjected to structural limitations which have led to less reliable performance.
In addition to the above problems, the conventional puncture detecting devices have suffered from a disadvantage in that the magnet is not supported in a stable manner, and is likely to wobble due to centrifugal forces, resulting in friction with surrounding parts. The devices thus tend to malfunction when the tire air pressure is reduced, and hence have a decreased degree of responsiveness and rapid puncture detection. When the magnet is accompanied by a shunt core that serves to absorb magnetic flux, if the magnet is accidentally moved from its proper position due to centrifugal forces the magnet and the shunt core tend to detach from one another. When the magnet has become displaced, a leakage of magnetic flux occurs. Where the magnet is supported by a diaphragm and is urged by a spring acting against the tire pressure, the magnet cannot be rapidly displaced forwardly in response to a reduction in the tire pressure. Thus, a relatively long interval of time is required for movement of the magnet toward the switch, precluding quick puncture detection by the device.
The present invention has been provided to overcome the above-discussed disadvantages and shortcomings associated with known puncture detecting devices.